Interpretive Summary: Imported fire ant populations with multiple-queen colonies are reported to be a much greater environmental and economic problem than populations with single-queen colonies because of much higher population densities associated with the multiple-queen form. This study compared population densities of multiple- and single-queen fire ants using measures of mound density, worker number, ant biomass, and metabolic consumption. Multiple-queen populations contained 1.94 times more workers per unit area (35 million versus 18 million workers/ha ) and 1.86 times more mass (27.7 versus 14.9 kg wet weight/ha) than single queen populations. Energy usage of the ants per hectare was 2.30 times higher in multiple-queen populations. Overall, This study indicates that fire ant populations with multiple-queens are about two times larger on average than populations with single-queen colonies. Presumably, this means that multiple-queen populations are about twice the economic, medical, and environmental problem in areas where they occur.

Technical Abstract:
Polygyne or multiple-queen fire ants (Solenopsis invicta Buren) are reported to be a substantially greater environmental and economic problem than monogyne or single-queen fire ants because of much higher population densities associated with polygyny. This study compared population densities of polygyne and monogyne fire ants using measures of mound density, worker number, ant biomass, metabolic consumption and standing caloric energy of ant biomass. We began the experiment by counting and measuring mounds at 14 polygyne and 14 monogyne sites located within a 35-km radius of Gainesville, Florida. Average mound densities were 3.03 times larger at polygyne sites than at monogyne sites (470 verses 155 mounds/ha). To adjust for differences in mound size, 22 monogyne and 21 polygyne mounds of various sizes were excavated from 16 of the experimental sites. Colony size and biomass were regressed on mound volume. These regressions were then used to estimate colony size and colony biomass from the mound volumes measured at the 28 field sites. The estimated colony sizes and colony biomasses at each site were summed and used to estimate field population densities. Polygyne populations contained 1.94 times more workers per unit area (35 million versus 18 million workers/ha ) and 1.86 times more biomass (27.7 versus 14.9 kg wet weight/ha) than monogyne populations. Energy usage and standing energy of the ants per hectare were respectively 2.30 times and 1.90 times higher in polygyne populations. Overall, This study indicates that polygyne population densities are about two times larger on average than monogyne population densities.